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Orion’s Footstool

StarDate:

February 1, 2014

The beautiful constellation Orion strides across the southern sky this evening. It’s in the southeast as night falls, with its brightest star, Rigel, to the lower right of its prominent three-star belt.

If the hunter ever gets tired during his perpetual journey across the sky, he can always prop his feet up for a little rest. That’s because a “footstool” has been provided for him in the adjoining constellation Eridanus, the river. The stool is marked by the moderately bright star Cursa. Its name comes from an Arabic phrase that means “the footstool.”

For the most part, Cursa is an unremarkable star. It’s a few times bigger and heavier than the Sun, and a few dozen times brighter. It’s used up the original hydrogen fuel in its core, so it’s undergoing a series of changes. The changes will cause its core to get smaller and hotter, igniting the next round of nuclear fusion. At the same time, its outer layers will get bigger and cooler. That will make Cursa shine much brighter than it does now. It’ll also give the star a definite orange hue.

One remarkable thing did happen to the star more than a quarter of a century ago. For a couple of hours, it flared to more than 10 times its normal brightness. But it hasn’t repeated the flare-up, so astronomers can’t explain its sudden showiness.

Cursa stands just above Orion’s foot — bright blue-white Rigel — in early evening, ready to give the hunter a break in his journey across the night sky.

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